Discharge lamps, in particular XBO® high pressure discharge lamps, have an ellipsoidal lamp bulb that surrounds an anode and a cathode. The service life of such discharge lamps is determined, inter alia, by the blackening of the lamp bulb that occurs during operation and leads to a substantial loss in useful light. The blackening has various causes. One of them is the evaporation of anode material on the basis of the high temperatures during operation of the high pressure discharge lamp, said material being deposited on the inner surface of the lamp bulb. A further cause of the blackening are contaminations of the gas fill in the lamp bulb, for example atmospheric residues such as oxygen and moisture that can be removed only with a high outlay on time and cost during the production of the high pressure discharge lamp.
There have been various approaches to date for minimizing the blackening. For example, use is made of relatively large lamp bulbs such that deposits can be distributed over a relatively large area, the blackening continuing to occur in weakened form, nevertheless. A further approach to this solution is to use large volume anodes in order to lower the anode temperature during operation by means of a large emission area, and thus to reduce the evaporation of anode material.